The present invention relates to a circuit arrangement for selecting a radioelectric signal from among a number of signals received by a signal receiver equipped with a character display device, the said arrangement enabling at least two selection modes of the said radioelectric signal and comprising a controllable oscillator the frequency of which is determined by a control loop depending on a binary number N supplied by a processing unit on the basis of coded input data, the said loop consisting of frequency dividing means for obtaining a first signal from the said controllable oscillator depending at least on the said number N, means for comparing the said first signal with a second frequency reference signal for obtaining a third signal for required tuning, memorising means with a number of cells for digital storage of data relative to the signals being tuned into and, means for supplying the said number N both in direct response to the said coded input data and by calling up data from the said memorising means.
The system commonly used on television receivers for tuning into the required channels is the so-called FREQUENCY SYNTHESIZER system. This system, made possible by the advent of integrated circuits, offers a number of advantages over other known systems, such as the conventional potentiometer type MECHANICAL MEMORY systems used until recently and also over the more recent so-called VOLTAGE SYNTHESIZER systems. The frequency synthesizer system is fully electronic enabling any channel to be called up directly by the user who formulates the channel number on a keyboard or other control device. The system usually consists of a quartz-controlled reference oscillator, a phase lock loop, a programmable divider and a computer which supplies the number to be sent to the programmable divider in response to the number of the channel set by the user. See, for example, U.S. Pat. No. 3,882,400.
Thanks to the phase lock loop, for each channel number set by the user, the frequency of the local oscillator on the set is kept so stable and accurate that the set is perfectly tuned to the corresponding channel signal. For further details about frequency synthesizer tuning systems, refer to the article entitled "A Frequency Synthesizer for Television Receivers" by E. G. Breeze, published in the November, 1974 issue of the "Transactions BTR" magazine, or "Digital Television Tuner Uses MOS LSI and Non Volatile Memory" by L. Penner, published in the Apr. 1, 1976 issue of "Electronics".
The frequency synthesizer system lends itself well to a plurality of different television channel tuning applications (hereinafter selection modes):
(1) direct selection by formulating the required channel number as described above (as is known, television channels are numbered: for example, on the European C.C.I.R. standard, V.H.F. band channels are numbered from 2 to 12 and U.H.F. band channels from 21 to 69: on the American standard VHF channels are numbered from 2 to 13 and UHF from 14 to 83). PA1 (2) memory selection; each of a certain set of keys corresponds to a given channel, selected and memorized beforehand. PA1 (3) automatic scanning of all the channels of a given standard, of all the channels contained in the memory or continuous scanning of all the frequency bands involved. PA1 (A) tuner means for tuning said television receiver to a frequency determined by a control signal applied thereto; PA1 (B) display means for displaying visual information; PA1 (C) control means operable in a direct selection tuning mode, a memory selection tuning mode and a memory display tuning mode; PA1 (D) a keyboard including a plurality of keys, said keyboard enabling the operator of said television receiver to select the mode of operation of said control means and to enter frequency data indicative of the desired tuning frequency of said tuner means; PA1 (E) memory means having a plurality of storage locations, each of said storage locations being capable of storing key information relating a respective one of said keys to a desired tuning frequency; and PA1 (F) said control means for: PA1 (A) a keyboard including a plurality of keys; PA1 (B) memory means for storing receiver operation information indicating a desired tuning frequency as well as other desired operating parameters of said television receiver; PA1 (C) said keyboard permitting the operator of said television receiver to enter said receiver operation information to be stored in said memory means and also to cause stored receiver operation information to be read out of said memory means; PA1 (D) control means responsive to the operation of said keyboard and operable in a first mode wherein new receiver operation information is read into said memory and a second mode wherein said stored receiver operation information is read out of said memory and causes said television receiver to be operated in accordance with said receiver operation information; PA1 (E) means for calculating a first numerical value corresponding to a predetermined combination of new receiver operation information as it is first stored in said memory means; PA1 (F) means for memorizing said first numerical value; PA1 (G) means for calculating a second numerical value corresponding to said predetermined combination of stored receiver operation information as said stored receiver information is read out of said memory; and PA1 (H) means for comparing said first and second numerical values.
The first application enables immediate, direct selection of any one of the channels on the relative standard (60 in Europe, 82 in America).
The second enables faster detection of one of a limited number of preferred channels.
The third is a fast, simple way of finding out which standard channels can be received, which channels have been memorized and whether other broadcasting stations exist on non-standard frequencies such as the private broadcasting stations in Italy (there are currently over a hundred operating).
Examples of frequency synthesizer systems with this wide range of selection modes are described in West German Patent Application Nos. 26 45 833 and 26 52 185 and, in particular, U.S. Patent Application Ser. No. 971,073.
All these modes, which are particularly useful in areas where a number of broadcasting stations can be received, require highly complex control equipment which many users may find difficult to operate. This is even more so if, besides emitter selection and standard receiver adjustment controls (volume, brightness, colour, etc.), provision is also made for additional accessory functions such as a digital clock which required additional setting controls.
An aim of the present invention is to provide a circuit arrangement for a television receiver enabling the many functions described above to be affected simply and cheaply with as little operating difficulty as possible on the part of the user.